1. Field of the Invention
The present invention relates to a mold changing apparatus for use in a tire vulcanizer having a plurality of mold stations.
2. Description of the Prior Art
A typical conventional tire vulcanizing press is equipped with a tire mold that accommodates tires to be produced. The tire mold requires the inner surface thereof to be washed periodically, and it also needs to be replaced in the middle of production to change the size of tires to be produced or the pattern formed on the tire surface. The tire mold, which is contaminated during production, is removed from the tire vulcanizing press for washing and remounted thereto after washing. The replacement is performed by releasing the top press-heating plate on the press side from the top half of the mold and the bottom press-heating plate on the press side from the bottom half of the mold (in many cases clamping is effected by using bolts), and taking the mold out of the press by use of a forklift truck or an overhead traveling crane, and then mounting a new mold by executing a procedure reverse to the above.
The above-described prior art involves problems stated below:
(1) Since mold clamping is effected by bolting, the operator is obliged to perform an inefficient operation in a bad environment.
(2) At the time of mounting the mold, it needs to be installed with high accuracy with respect to the press, and it is therefore necessary to fit the mold to a projecting ring portion, known as "register ring", which is provided on the press. Since the gap between the projecting ring and the mold is 0.5 mm or less, the mold mounting process involves an inefficient operation in which an assistant to the operator of the forklift or the crane lowers the suspended mold while swinging it for engagement with the projecting ring.
(3) It is an ideal practice for the mold replacement to remove the mold immediately after the vulcanization of the final tire produced by this mold and to start production with a new mold immediately after it has replaced the old one. In actuality, however, the arrival of a new tire which is to be mounted may cause delay, or the disposition of an assistant operator may cause delay, resulting in a loss of time. In addition, a mold which is to be mounted is in a cooled state, or even if it has been preheated, in many cases the press is remote from the mold yard. Therefore, when mounted, the new tire mold has not yet been heated to such an extent that the production can be started immediately. Accordingly, it is necessary to perform a preheating operation in the press after the replacement, resulting in a lowering of the productivity.
The prior art further suffers from the following problem.
The conventional tire vulcanizing press comprises various constituent devices, such as devices that function only during the vulcanizing cycle, devices that function only during the loading and unloading cycle, and devices that function during both the cycles.
In the case of small-sized tires for automobiles, for example, the vulcanizing cycle is about 10 minutes, while the loading and unloading cycle is about 1 minute. In other words, the loading and unloading process accounts for only about 10% of the production cycle, whereas the percentage of the total installation cost that is taken up by the loading and unloading equipment exceeds this level by a large margin. In the case of producing recent high-accuracy tires, the cost proportion of the loading and unloading equipment is higher than that in the case of production of conventional tires. In particular, the shaping method (part of the loading process) disclosed in Japanese Patent Laid-Open (KOKAI) No. 02-200405 (1990) needs a complicated mechanism, which is not provided in the conventional press, so that the proportion taken up by the loading and unloading cost is high, although this method has been proved by an actual machine to be suitable for production of tires of higher accuracy.